swift - How to apply audio effect to a file and write to filesystem - iOS -

i'm building app should allow user apply audio filters recorded audio, such reverb, boost.

i unable find viable source of information on how apply filters file itself, because it's needed upload processed file server later.

i'm using audiokit visualization, , i'm aware it's capable of doing audio processing, playback. please give suggestions further research.

you can use newly-introduced "manual rendering" features audio unit plugins (see example below).

if need support older macos/ios version, surprised if can't achieve same audiokit (even though haven't tried myself). instance, using aksampleplayer first node (which read audio file), building , connecting effects , using aknoderecorder last node.

example of manual rendering using new audio unit features

import avfoundation  //: ## source file //: open audio file process let sourcefile: avaudiofile let format: avaudioformat {     let sourcefileurl = bundle.main.url(forresource: "mixloop", withextension: "caf")!     sourcefile = try avaudiofile(forreading: sourcefileurl)     format = sourcefile.processingformat } catch {     fatalerror("could not open source audio file, \(error)") }  //: ## engine setup //:    player -> reverb -> mainmixer -> output //: ### create , configure engine , nodes let engine = avaudioengine() let player = avaudioplayernode() let reverb = avaudiounitreverb()  engine.attach(player) engine.attach(reverb)  // set desired reverb parameters reverb.loadfactorypreset(.mediumhall) reverb.wetdrymix = 50  // make connections engine.connect(player, to: reverb, format: format) engine.connect(reverb, to: engine.mainmixernode, format: format)  // schedule source file player.schedulefile(sourcefile, at: nil) //: ### enable offline manual rendering mode {     let maxnumberofframes: avaudioframecount = 4096 // maximum number of frames engine asked render in single render call     try engine.enablemanualrenderingmode(.offline, format: format, maximumframecount: maxnumberofframes) } catch {     fatalerror("could not enable manual rendering mode, \(error)") } //: ### start engine , player {     try engine.start()     player.play() } catch {     fatalerror("could not start engine, \(error)") } //: ## offline render //: ### create output buffer , output file //: output buffer format must same engine's manual rendering output format let outputfile: avaudiofile {     let documentspath = nssearchpathfordirectoriesindomains(.documentdirectory, .userdomainmask, true)[0]     let outputurl = url(fileurlwithpath: documentspath + "/mixloopprocessed.caf")     outputfile = try avaudiofile(forwriting: outputurl, settings: sourcefile.fileformat.settings) } catch {     fatalerror("could not open output audio file, \(error)") }  // buffer engine render processed data let buffer: avaudiopcmbuffer = avaudiopcmbuffer(pcmformat: engine.manualrenderingformat, framecapacity: engine.manualrenderingmaximumframecount)! //: ### render loop //: pull engine desired number of frames, write output destination file while engine.manualrenderingsampletime < sourcefile.length {     {         let framestorender = min(buffer.framecapacity, avaudioframecount(sourcefile.length - engine.manualrenderingsampletime))         let status = try engine.renderoffline(framestorender, to: buffer)         switch status {         case .success:             // data rendered             try outputfile.write(from: buffer)          case .insufficientdatafrominputnode:             // applicable if using input node 1 of sources             break          case .cannotdoincurrentcontext:             // engine not render in current render call, retry in next iteration             break          case .error:             // error occurred while rendering             fatalerror("render failed")         }     } catch {         fatalerror("render failed, \(error)")     } }  player.stop() engine.stop()  print("output \(outputfile.url)") print("avaudioengine offline rendering completed") 

you can find more docs , examples updates audiounit format there.

wiki